1. Field of the Invention
The present invention relates to an apparatus and method of controlling a power in a mobile communication system, and more particularly to an apparatus and method of controlling forward link power while in discontinuous transmission mode.
2. Description of the Related Art
Typically, discontinuous transmission mode (DTX) is a mode that transmits data in a frame unit only when there is data to be transmitted in a wired system or a mobile communication system. Discontinuous transmission mode is used for the following advantages. Since data frames are transmitted only when data actually exists, transmission power can be minimized, and the strength of the interference signal affecting the system is reduced, so that the capacity of the whole system is increased.
However, since the transmitter discontinuously transmits frames, the receiver cannot recognize whether a frame is transmitted, and this causes a base station not to be able to perform forward link power control by itself. Specifically, when the receiver of a terminal cannot accurately judge whether a frame is transmitted, the receiver of the terminal cannot trust judgment variables of a decoder including a cyclic redundancy code (CRC) and so on, and the result of decoding decision of its decoder. Since the result of judgment cannot be trusted, the existing method used in continuous transmission mode cannot accurately control the transmission power of the base station when in discontinuous transmission mode. Hereinafter, an example of the conventional forward link power control method performed in the receiver of the discontinuous transmission mode mobile radio communication system will be explained.
FIG. 1 is a block diagram of the conventional forward link power control apparatus of the receiver and the transmitter in the discontinuous transmission mode mobile communication system. Here, it is assumed that the mobile communication system is a code division multiple access (CDMA) communication system.
Referring to FIG. 1, a radio frequency (RF) section 10 converts an RF signal received through an antenna ANT into a baseband frequency by frequency-down-converting the RF signal. A receiver 12 despreads the output signal of the RF section 10, and determines the level of a symbol by accumulating the despread signals in a symbol unit. At this time, the despreading includes PN despreading and orthogonal despreading. A decoder 14 of the receiver checks whether the received frame is in a good state or in an erasure state by checking the received frame thereby checking the condition of the channel. A control section 16 transmits the result of checking from the decoder 14 backward to the base station. When the result of channel checking, which is transmitted backward to a power control section (not illustrated in FIG. 1) of the base station, is in a good state, the power control section judges that the channel is in a good state, and reduces the forward transmission power. On the other hand, when the result of channel checking is in an erasure state, the judgment of the power control section depends on whether the base station had transmitted a prior frame. If the base station had transmitted a prior frame, the power control section judges that the channel is in an erasure state, and increases the forward transmission power, while if the base station has not transmitted a prior frame, the power control section ignores the result and thus does not reflect the command in the forward link power control.
Accordingly, when in discontinuous transmission mode, the conventional forward link power control method has the drawback that the forward link power control command that is transmitted backward is used only when the transmitted data frame exists, the speed at which the forward link power control is adjusted becomes greatly lowered. In other words, when in discontinuous transmission mode where the amount of transmitted data is very small, power control is performed at a very low speed that is much less than the power control speed of 50 Hz in continuous transmission mode, and thus the forward link power control cannot follow the speed of the channel change. As a result, an apparatus and method of more rapidly and accurately controlling the forward link power when in discontinuous transmission mode are needed.